This invention relates to the field of vibration damping and isolation. In particular, the present invention is a passive damping and isolation system that uses direct shear of a viscous fluid to dampen vibration energy.
A precision structural system carrying a load, such as a telescope, is susceptible to disturbances that produce structural vibrations. Such vibrations may be contributed to the structural system by components or assemblies of the system itself. For example, reaction wheel assemblies used to point the telescope. Since such a precision structural system tends to have little inherent damping, these vibrations can lead to serious performance degradation. Therefore, an efficient means of damping and isolating, in a controlled manner, the load carried by a precision structural system is of considerable importance.
Typically, to minimize performance degradation caused by vibrations, passive damping and isolation systems (otherwise known as "fluid dampers") have been used for damping and isolating the load carried by a precision structural system. Present fluid dampers operate by displacing a viscous fluid from one fluid reservoir to another fluid reservoir through a restrictive passage. Shearing of the viscous fluid as it flows through the restrictive passage provides a damping force that is proportional to velocity. This requires that the restrictive passage be relatively long with respect to its cross-section so that the damping force is proportional to velocity, and not due to restrictive passage entrance and exit fluid pressure drops or turbulent to laminar flow regimes. In addition, the mass of the viscous fluid within the restrictive passage must be minimized to prevent non-linear fluid surge effects.
To function properly, one of the fluid reservoirs must be pressurized with respect to the other fluid reservoir to force the viscous fluid to flow from one reservoir to the other through the restrictive passage. This pressurization must be contained by the fluid damper structure for the fluid damper to operate consistently over its useful life. To prevent leakage of the viscous fluid, hermetic seals must be used. These hermetic seals must be designed to withstand the internal fluid pressure of the damper, and may add volumetric compliance to the damping and isolation system. This volumetric compliance may be beneficial in isolation systems but reduces the performance of pure dampers. In addition, since typical rubbing type, hermetic seals add undesirable stiction to the damper, non-stiction hermetic seals, such as bellows, must be incorporated into the fluid damper. These bellows see an internal fluid pressure proportional to velocity making them susceptible to failure under high shock loads. All of these concerns (i.e., viscous fluid flow considerations related to the restrictive passage, fluid seal considerations related to pressurization of the viscous fluid and non-linearities due to fluid mass effects) often drive the design of the damping and isolation system requiring additional system size and weight and/or system complexity.
There is a need for improved damping and isolation systems. In particular, there is a need for a damping and isolation system that will virtually eliminate system design concerns related to the damping force provided by the flow of viscous fluid through the restrictive passage. Moreover, there is a need for a damping and isolation system that will essentially eliminate system operation concerns of viscous fluid leakage related to pressurization of the viscous fluid during operation of the damping and isolation system. The damping and isolation system should surmount these concerns while maintaining a weight, size and complexity efficient structure.